1. Field of the Invention
This invention relates in general to methods for optically identifying concentration of substances that can be directly observed in a medium using the inherent color of the substance or by indirectly observing the substance with the use of a color indicator.
2. Description of Related Art
There are many different physical chemical methods which can be utilized for identifying concentration of a substance for example, in a light medium. In most instances, however, involved methods are complicated and large and stationary apparatus are needed for this purpose. Thus, exact concentration measurements are usually only possible in a laboratory and are carried out there using spectrometers, gas chromatographs, elementary analyzers and other expensive and complicated apparatus.
When there is a problem of measuring concentration quickly outside of the laboratory as, for example, outdoors, than optical methods can be utilized for a number of such measurements. For example, the use of the colorations of the substance to be measured which are dependent on the specific concentrations of the substance or the use of a color indicator that responds to this substance can be used. An example of such an indication is that of pH value measurement using color indicators. The color indicators are substances which change color or loose their color at different pH values.
Since only two pH regions can be distinguished using a single indicator, suitable mixtures of indicators are currently used which yield a hue which varies over a greater pH value range. For identifying the exact value, this hue is compared to a color scale and the pH value is then read from the color scale.
This evaluation method using color comparison however, is extremely subjective and is significantly more difficult if not impossible if further color substances or a contaminate, for example, waste water, are present in the sample solution.
See also U.S. Pat. Nos. 4,560,275, 4,484,817, 4,677,289, 4,267,572, Patent Abstracts of Japan, Vol. 6, No. 217 (P-152) 1095 Oct.30, 1982 No. 57-120829,Matsushita Denki Sangyo, Patent Abstracts of Japan, Vol. 9,No. 37 (P-335) (1760) Feb. 16, 1985, No. 59-180310,Fijitsu KK, the article by W. Albertshofer, A. Gerhard, Flussigkeitsanalyse unter Verwendung einer Spektrometer diode, Proceedings of Sensoren-Technologie und Anwendung, Bad Nauheim, FRG, 1986, NTG-Fachberichte 93, appendix, page 30,German Application No. DE P 37 36 201.1, German application No. DEP3743 131.5 which corresponds to U.S. application Ser. No. 261,489 and German application P 37 36 203.8.